Forming white metal oxide films by oxide structure modification or subsurface cracking

ABSTRACT

The embodiments described herein relate to forming white appearing metal oxide films by forming cracks within the metal oxide films. In some embodiments, the methods involve directing a laser beam at a metal oxide film causing portions of the metal oxide film to melt, cool, contract, and crack. The cracks have irregular surfaces that can diffusely reflect visible light incident a top surface of the metal oxide film, thereby imparting a white appearance to the metal oxide film. In some embodiments, the cracks are formed beneath a top surface of a metal oxide film, thereby leaving a continuous and uninterrupted metal oxide film top surface.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This Application is a continuation of U.S. application Ser. No.14/261,060, filed Apr. 24, 2014, entitled “FORMING WHITE METAL OXIDEFILMS BY OXIDE STRUCTURE MODIFICATION OR SUBSURFACE CRACKING,” issuedDec. 12, 2017 as U.S. Pat. No. 9,839,974, which claims the benefit ofU.S. Provisional Application No. 61/903,890 filed Nov. 13, 2013,entitled “FORMING WHITE METAL OXIDE FILMS BY OXIDE STRUCTUREMODIFICATION OR SUBSURFACE CRACKING,” the contents of which areincorporated by reference herein in their entirety for all purposes.

FIELD

This disclosure relates generally to metal oxide films. Morespecifically, methods for producing white appearing metal oxide filmsusing subsurface cracking techniques are disclosed.

BACKGROUND

Metal surfaces of many consumer products are often protected with a thinfilm of metal oxide. The metal oxide is generally harder than theunderlying metal and thus provides a protective coating for the metal.Often, the metal oxide film is formed using an anodizing process.Anodizing is an electrolytic process that increases the thickness of anatural oxide layer on the surface of metal parts. The metal part to betreated forms an anode of an electrical circuit such that the surface ofthe metal part is converted to a metal oxide film, also referred to asan anodic film. The anodic film can also be used for a number ofcosmetic effects. For example, techniques for colorizing anodic filmshave been developed that can provide an anodic film with a perceivedcolor based. A particular color can be perceived when a light of aparticular range of frequencies is reflected off the surface of theanodic film.

In some cases, it can be desirable to form an anodic film having a whitecolor. However, conventional attempts to provide white appearing anodicfilms have resulted in anodized films that appear to be off-white, mutedgrey, and yellowish white instead of a crisp appearing white that manypeople find appealing.

SUMMARY

In one aspect, a method of modifying an appearance of an oxide filmdisposed on a substrate surface is described. The oxide film may be madeof metal oxide material. The method may include forming at least onemelted portion by heating the metal oxide material within a portion ofthe oxide film to a melting temperature of the metal oxide material. Themethod may further include creating several cracks within the oxide filmby allowing the melted portion to cool and contract. Each of the severalcracks is positioned substantially entirely beneath a top surface of theoxide film. The several cracks within the oxide film cause visible lightincident a top surface of the oxide film to scatter imparting a whiteappearance to the oxide film.

In another aspect, a part is described. The part may include a metalsubstrate and a metal oxide layer. The metal substrate may include asubstrate surface, the substrate surface having a mirror finish thatspecularly reflects substantially all visible light incident thesubstrate surface. The metal oxide layer disposed on the metalsubstrate, the metal oxide layer having a bottom surface adjacent thesubstrate surface and a top surface opposite the bottom surface. Themetal oxide layer may include a first portion that is substantiallytranslucent to visible light incident the top surface of the oxide layersuch that at least a portion of visible light incident the top surfacetravels through the first portion and specularly reflects off thesubstrate surface. The metal oxide layer may also include a secondportion having several cracks positioned beneath the top surface.Visible light incident the top surface of the oxide film diffuselyreflects off the several cracks imparting a white quality to the secondportion.

In another aspect, an enclosure for an electronic device is described.The enclosure may include a substrate and an oxide layer. The substratemay have several protrusions forming a first roughness. The oxide layermay be formed over the several protrusions. The oxide layer may includea first portion having several crystalline portions. A first light rightray reflected by the several crystalline structures forms a firstappearance, and a second light ray absorbed by the several protrusionsof a first roughness forms a second appearance. The second appearancemay be different from the first appearance.

Other systems, methods, features and advantages of the embodiments willbe, or will become, apparent to one of ordinary skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional systems, methods, features andadvantages be included within this description and this summary, bewithin the scope of the embodiments, and be protected by the followingclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detaileddescription in conjunction with the accompanying drawings, wherein likereference numerals designate like structural elements, and in which:

FIGS. 1A-1D illustrate various reflection mechanisms for providing aperceived color or quality of an object;

FIG. 2A shows a cross section of a portion of part that includes anoxide layer with crystalline metal oxide portions that diffusely reflectincident light and give the oxide layer a white appearance;

FIG. 2B shows a cross section of a portion of part that includes anoxide layer with cracks that diffusely reflect incident light and givethe oxide layer a white appearance;

FIGS. 3A-3C show cross section views of a portion of part that includesan oxide layer undergoing a laser melting procedure in accordance withdescribed embodiments;

FIGS. 4A and 4B show cross section views of different parts undergoingdifferent types of laser melting procedures in accordance with describedembodiments;

FIGS. 5A-5C show cross section and top views of different parts havingoxide layers with different patterns of spots of crystalline metal oxideor cracks;

FIGS. 6A-6C show cross section and top views of different parts havingoxide layers with different patterns of lines of crystalline metal oxideor cracks;

FIGS. 7A-7C show cross section views of different parts having oxidelayers with spots of crystalline metal oxide or cracks positioned atdifferent depths within the oxide layers;

FIG. 8 shows a flowchart indicating a method for forming a white oxidelayer using a melting process in accordance with described embodiments;

FIG. 9A shows a cross section view of a part with a first portion thatdiffusely reflects incident light and a second portion that specularlyreflects light;

FIG. 9B shows a flowchart indicating a method for tuning a meltingprocess for producing a white oxide film having a target amount ofdiffuse and specular reflectance;

FIG. 10 shows a cross section view of a portion of a part with an oxidelayer having light diffusing spots positioned over a substrate having aroughed surface;

FIG. 11 shows a top view of a part with an oxide layer having lightdiffusing spots and having different colored portions and in accordancewith described embodiments;

FIG. 12 shows a top view of a part with an oxide layer having lightdiffusing spots and having different dyed portions and in accordancewith described embodiments; and

FIG. 13 shows a flowchart indicating a method for forming an oxide layeron a part having a particular optical quality using the describedmelting methods.

Those skilled in the art will appreciate and understand that, accordingto common practice, various features of the drawings discussed below arenot necessarily drawn to scale, and that dimensions of various featuresand elements of the drawings may be expanded or reduced to more clearlyillustrate the embodiments of the present invention described herein.

DETAILED DESCRIPTION

Reference will now be made in detail to representative embodimentsillustrated in the accompanying drawings. It should be understood thatthe following descriptions are not intended to limit the embodiments toone preferred embodiment. To the contrary, it is intended to coveralternatives, modifications, and equivalents as can be included withinthe spirit and scope of the described embodiments as defined by theappended claims.

This application relates to various methods and apparatuses used fortreating a metal oxide film such that the metal oxide film appearswhite. In some embodiments, methods involve modifying at least a portionof the metal oxide film to a crystalline form metal oxide. In someembodiments, methods involve creating cracks or small gaps within themetal oxide film and beneath a top surface of the metal oxide film. Insome embodiments, methods involve creating crystalline portions combinedwith creating cracks. The crystalline metal oxide or cracks within themetal oxide can interact with visible light incident the top surface ofthe film to give the metal oxide film a white appearance. The whiteappearing metal oxide films are well suited for providing protective andattractive surfaces to visible portions of consumer products. Forexample, methods described herein can be used for providing protectiveand cosmetically appealing exterior portions of metal enclosures andcasings for electronic devices, such as those manufactured by AppleInc., based in Cupertino, Calif.

As used herein, the terms oxide film, oxide layer, metal oxide film, andmetal oxide layer may be used interchangeably and can refer to anyappropriate metal oxide material. In some embodiments, the oxide film isformed using an anodizing process and can be referred to as an anodicfilm or anodic layer. The metal oxide films are formed on metal surfacesof a metal substrate. The metal substrate can include any of a number ofsuitable metals. In some embodiments, the metal substrate includes purealuminum or aluminum alloy. In some embodiments, suitable aluminumalloys include 1000, 2000, 5000, 6000, and 7000 series aluminum alloys.

In general, white is the color of objects that diffusely reflect nearlyall visible wavelengths of light. Thus, a metal oxide film can beperceived as white when nearly all visible wavelengths of light incidenta top surface of the metal oxide film are diffusely reflected. FIG. 1A,shows how incident light can be diffusely reflected off a surface andscattered in many directions. Diffuse reflection can be caused byincident light reflecting off multi-faceted surfaces at a top surface orwithin an object. For example, facets of ice crystals that form asnowflake diffusely reflect incident light, rendering the snowflakewhite in appearance. This is in contrast to specular reflection (FIG.1B) where light is reflected in one direction, colored objects (FIG. 1C)where some wavelengths of light are absorbed and only certainwavelengths of light are diffusely reflected, and black objects (FIG.1D) where substantially all the wavelengths of light are absorbed and nolight is reflected.

The amount of perceived whiteness of a metal oxide film can be measuredusing any of a number of color analysis techniques. For example a coloropponent process scheme, such as an L,a,b (Lab) color space based in CIEcolor perception schemes, can be used to determine the perceivedwhiteness of different oxide film samples. The Lab color scheme canpredict which spectral power distributions (power per unit area perwavelength) will be perceived as the same color. In a Lab color spacemodel, L indicates the amount of lightness, and a and b indicatecolor-opponent dimensions. In some embodiments described herein, thewhite metal oxide films have L values ranging from about 85 to 100 anda,b values of nearly zero. Therefore, these metal oxide films are brightand color-neutral.

Some embodiments described herein involve forming crystalline portionsof metal oxide within an oxide film such that incident light diffuselyreflects off interfaces created by the crystalline portions, therebyimparting a white appearance to the oxide film. To illustrate, FIG. 2Ashows a cross section of a portion of part 200, which includes substrate202 and oxide layer (or oxide film) 204. Oxide layer 204 can be aglass-like amorphous metal oxide material 205 that is substantiallytranslucent or transparent to visible light. Oxide layer 204 includescrystalline portion 220, which has a different structure thansurrounding amorphous metal oxide material 205. Crystalline portion 220includes multiple metal oxide crystals, each having light reflectivefacets. Incoming visible light can reflect off the crystalline facets atdifferent angles, causing the light to scatter and diffusely reflect.For example, light ray 210 can enter oxide layer 204, reflect off of afirst crystalline facet of crystalline portion 220 oriented at a firstangle relative to top surface 208, and exit oxide layer 204. Light ray212 can enter oxide layer 204, reflect off of a second crystalline facetof crystalline portion 220 oriented at a second angle different from thefirst angle relative to top surface 208, and exit oxide layer 204. Inthis way, multiple light rays entering oxide layer 204 can reflect offof crystalline portion 220 at multiple different angles, causing lightto be diffusely reflected off of crystalline portion 220, therebyimparting a white appearance to oxide layer 204. In addition, thecrystalline form of metal oxide within crystalline portion 220 will havea different refractive index compared to surrounding amorphous metaloxide material 205, which can cause further diffraction of lightincident top surface 208 and contribute to the white appearance of oxidelayer 204. Note that in some embodiments, substantially the entire oxidelayer 204 is transformed to a crystalline form.

As shown in FIG. 2B, in some embodiments, crystalline portion 220 hascracks 206 formed therein such that incident light diffusely reflectsoff of interfaces of the cracks, thereby contributing a white appearanceto the oxide film. In some embodiments, cracks 206 are formed withoutformation of crystalline portion 220. Cracks 206 are breaks in the metaloxide material of oxide layer 204. Cracks 206 have surfaces that areirregularly oriented within oxide layer 204. Incoming visible light canreflect off the irregularly oriented surfaces at different angles,causing the light to diffusely reflect off of cracks 206. For example,light ray 211 can enter oxide layer 204, reflect off of a first surfaceof cracks 206 oriented at a first angle relative to top surface 208, andexit oxide layer 204. Light ray 213 can enter oxide layer 204, reflectoff of a second surface of cracks 206 oriented at a second angledifferent from the first angle relative to top surface 208, and exitoxide layer 204. In this way, multiple light rays entering oxide layer204 can reflect off of cracks 206 at multiple different angles, causinglight to be diffusely reflected off of cracks 206, thereby imparting awhite appearance to oxide layer 204.

Crystalline portion 220 and cracks 206 can have any suitable shape andsize. As described above, crystalline portion 220 can include a portionor make up substantially the entire metal oxide material of oxide layer204. If substantially the entire metal oxide material of oxide layer 204is in a crystalline form, cracks 206 can be formed throughout oxidelayer 204. Note that the size of cracks 206 are generally smaller thanas depicted in FIG. 2B with respect to an overall thickness of oxidelayer 204. In some embodiments, individual features of cracks 206 aresubstantially non-visible to an observer, but rather give at least aportion of oxide layer 204 a generally white appearance. In someembodiments, the lengths of cracks 206 are on the scale of micrometers(microns) or longer. In some embodiments, cracks 206 are on the scale ofbetween about 0.5 and 30 microns in length. In some embodiments, cracks206 form air-filled voids within oxide layer 204. The air within thevoids has a different refractive index than the surrounding metal oxidematerial, which can cause further diffraction of light. Note that cracks206 can have any suitable shape. In some embodiments, cracks 206 areelongated, as shown in FIG. 2B. In some embodiments, the cracks arecircular, elliptical (spherical or ellipsoidal) or pore-like in shape.Crystalline portion 220 or cracks 206 can be in any suitable locationwithin oxide layer 204. In some embodiments, substantially the entiretyof crystalline portion 220 or cracks 206 is positioned beneath topsurface 208 of oxide layer 204. Forming cracks 206 subsurface of topsurface may be used in applications wherein it is undesirable for topsurface 208 to have cracks. For instance, in some applications it may bedesirable to have a continuous and uninterrupted top surface 208. Insome embodiments, top surface 208 is smooth, shiny and specularlyreflective.

Crystalline portion 220 or cracks 206 can be formed using any suitableprocedure. In some embodiments, crystalline portion 220 or cracks 206are formed using a laser procedure. In some embodiments, crystallineportion 220 and cracks 206 are formed using other heating processes suchas a plasma process. In some embodiments, the laser is tuned to formcrystalline portion 220 or cracks 206 within oxide layer 204 between thetop surface 214 of substrate 202 and top surface 208 of oxide layer 204.This can be accomplished by directing a laser beam at oxide layer 204such that energy from the laser beam is focused on local areas withinoxide layer 204. The energy causes the metal oxide material in the localareas to melt. As the melted oxide material cools, it can re-solidify ina crystalline form. In some embodiments, the cooling process can formcracks 206. To illustrate, FIGS. 3A-3C show cross section views of aportion of part 300, which includes oxide layer 304 integrally formed onsubstrate 302, undergoing a laser procedure in accordance with describedembodiments.

At 3A, laser beam 310 is directed at top surface 308 of oxide layer 304.Laser beam 310 is tuned to generate enough heat to melt localizedportions of the metal oxide material of oxide layer 304. In someembodiments, laser beam 310 is scanned over substantially the entire topsurface 308 of oxide layer 304 to melt substantially all of oxide layer304. Laser beam 310 parameters such as wavelength, spatial energydistribution (e.g., spot size and beam shape), and temporal energydistribution (e.g., pulse duration and pulse separation) can be adjustedto cause a sufficient amount of energy to heat and melt the metal oxidebut not so high an energy to negatively impact the structural integrityof oxide layer 304 too much. In some embodiments, the metal oxidematerial within oxide layer 304 is heated to a temperature of about 600degrees C. or greater. In some embodiments, the metal oxide materialwithin oxide layer 304 is heated to a temperature ranging between about600 and 1200 degrees C. In some embodiments, the wavelength of laserbeam 310 ranges within the infrared spectrum of light. In someembodiments, a CO2 laser is used, which produces infrared laser lighthaving principle wavelength bands centering around 9.4 and 10.6micrometers.

Laser beam 310 is tuned such that depth of focus (DOF) 318 is positionedwithin oxide layer 304 between top surface 308 of oxide layer 304 andtop surface 314 of substrate 302. In some embodiments, spot size oflaser beam 310 is small enough to melt localized portions within oxidelayer 304 without substantially affecting surrounding portions of metaloxide material. In general, a smaller spot size corresponds to a smallerbeam waist 317, a larger beam width 316, a smaller DOF 318, and a higherenergy density (e.g., Joules/cm2). In some embodiments, the spot sizeand DOF 318 are each less than about 10 micrometers. In someembodiments, the spot size and DOF 318 each range from about onemicrometer and about 10 micrometers. It should be noted that the spotsize and DOF 318 used in the applications described herein for meltinglocalized portions within a metal oxide film are generally smallcompared to traditional laser ablating and marking procedures. Forexample, typical laser marking applications use a spot size in the rangeof about 20 micrometers and 100 micrometers and a DOF 318 in the rangeof about 100 micrometers to about 200 micrometers. In addition, the beamwidth 316 used in the applications described herein are generally largecompared to traditional laser ablating and marking procedures. In someembodiments, the shape of laser beam 310 is adjusted to optimize theeffect of laser beam 310 on oxide layer 304. For example, a Gaussianbeam shape (as shown in FIG. 3A) can have a different effect on themetal oxide material within oxide layer 304 compared to a flat top beamshape.

FIG. 3B shows spot 320, which corresponds to the area within oxide layer304 that is melted by an impinging laser beam. The diameter of spot 320can vary depending on laser parameters, such as those described above,as well as the nature of the metal oxide material of oxide layer 304. Insome embodiments, spot 320 has a diameter ranging from about 1micrometer and about 5 micrometers. In some embodiments, spot 320 has adiameter ranging from about 2 micrometers and about 5 micrometers. Thedepth 322 of spot 320 relative to top surface 308 of oxide layer 304 canbe adjusted using a number of methods. In some embodiments, anadditional laser system is used to measure thickness 323 of oxide layer304 prior to the laser cracking procedure. The measurement of thickness323 can then be used to adjust laser parameters of the laser used toperform the laser procedure such that spot 320 is positioned within adepth 322 that is predetermined within oxide layer 304. In someembodiments, top surface 308 is substantially planar such that depth 322is substantially constant throughout the area of top surface 308. As thelaser beam is directed at oxide layer 304, the energy of the laser beamgenerates localized heat within spot 320 of oxide layer 304 sufficientto at least reach the glass transition temperature of the metal oxidematerial within spot 320. Accordingly, at least a portion of the metaloxide material within spot 320 melts. In some embodiments, as heatgenerated by the laser beam dissipates and the metal oxide materialwithin spot 320 cools, the metal oxide material transitions to acrystalline form. In some embodiments, the amorphous form of metal oxidematerial is a hydroxide or hydrated form of aluminum oxide, such asboehmite. The heat from the laser beam can drive off water from thehydroxide or hydrated form of the aluminum oxide, leaving a crystallineform of aluminum oxide (i.e., alumina). As described above, lightincident top surface 308 of oxide layer 304 can diffusely reflect off ofthe crystalline facets within spot 320 and give oxide layer 304 a whiteappearance.

FIG. 3C shows spot 320 having cracks 306 formed therein. In someembodiments, during the cooling of metal oxide material within spot 320,the metal oxide material contracts forming cracks 306. The size ofcracks 306 can vary depending upon a number of parameters includinglaser energy parameters, cooling time, and type of oxide layer 304. Insome embodiments, cracks 306 are on the scale of between about 0.5 and30 microns in length. As described above, light incident top surface 308of oxide layer 304 can diffusely reflect off of the irregular surfacesof cracks 306 and give oxide layer 304 a white appearance.

As described above, in some embodiments, oxide layer 304 can be formedusing any suitable method. In some embodiments, methods such as plasmaelectrolytic oxidation are used to form oxide layer 304 that is inlargely crystalline form. In some embodiments, an anodizing process isused to form oxide layer 304 that is in largely amorphous form. In someembodiments, the laser is tuned to reflect off of the top surface of anunderlying substrate and back onto the oxide layer to cause meltingwithin the oxide layer. To illustrate, FIG. 4A shows a cross sectionview of a portion of part 400, which includes oxide layer 404 positionedon substrate 402. Laser beam 410 is tuned such that the depth of focus418 of laser beam 410 is positioned below oxide layer 404, i.e., belowtop surface 414 of substrate 402. Laser beam 410 then reflects off oftop surface 414 of substrate 402 and becomes focused at spot 420 withinoxide layer 404, thereby causing spot 420 of crystalline metal oxide orcracks 406 to form. As with the embodiments described above withreference to FIGS. 3A-3C, the crystalline metal oxide and/or cracks 406within spot 420 can cause light incident top surface 408 to diffuselyreflect off of the surfaces of the crystalline metal oxide or cracks 406and give oxide layer 404 a white appearance.

In some embodiments, the laser beam is directed at an oxide layer at anon-normal angle relative to a top surface of the oxide layer. FIG. 4Bshows a cross section view of a portion of part 450, which includesoxide layer 454 positioned on substrate 452. As shown, part 450 isskewed relative to beam path 456 of laser beam 460. That is, top surface458 of part 450 is positioned at a non-perpendicular angle 457 relativeto beam path 456. One advantage of using such a skewed configuration isthat laser beam 460 can impinge upon a greater effective thickness 462of oxide layer 454 compared to the actual thickness 464 of oxide layer454. In some embodiments, this allows for greater control over the depthof spot 466 within oxide layer 454.

An amount of whiteness of an oxide film can be adjusted by choosing anamount of spots of crystalline metal oxide material or cracks within theoxide film, the spatial distances between the spots within the oxidefilm, and the depth of the spots within the oxide film. The spots can beformed in patterns within an oxide films. In some embodiments, the spotsare formed in clusters within spots as described above with reference toFIGS. 3 and 4. In other embodiments, the cracks are formed insubstantially continuous lines. FIGS. 5-7 show cross section and topviews of different parts having different amounts of spots, differentpatterns of spots, and spots that are positioned in different locationswithin oxide films.

FIG. 5A shows a cross section view of part 500, which includes oxidelayer 504 disposed on substrate 502. Oxide layer 504 includes spots 506,which correspond to crystalline metal oxide portions or clusters ofcracks created by a laser operation as described above. Spots 506 arepositioned an average distance 509 from each other, sometimes referredto as pitch. Pitch 509 can be chosen such that the overall appearance ofoxide layer 504 is white as viewed from top surface 508. In someembodiments, the pitch is about twice the diameter 511 of spots 506. Insome embodiments, pitch 509 ranges from about 1 micrometer and about 10micrometers. In some embodiments, spots 506 are spaced equidistantlyfrom each other while in other embodiments spots 506 are spaced atsubstantially random distances from each other. The whiteness of oxidelayer 504 can be chosen by adjusting pitch 509, with smaller pitchescorresponding with whiter appearing oxide layers. Spots 506 can beformed using a pulsed laser beam or a continuous laser beam. Forexample, each spot 506 can correspond to a pulse of a pulsed laser beam,which is scanned over top surface 508. The laser beam can pulsed one ormore time at each of spots 506. If a continuous laser beam is used, thelaser beam can be positioned over each of spots 506 for a predeterminedtime period and moved quickly over distances between each of spots 506.Alternatively, mirrors can be used to position a continuous laser beamat locations corresponding to each spot 506.

FIGS. 5B and 5C show top views of different parts 510 and 520,respectively, having different patterns of spots of crystalline metaloxide portions or clusters of cracks. FIG. 5B shows a top view of part510 having equidistant spots 516 within oxide layer 514 that are spacedan average distance 519 apart from each other. Pitch 519 can be adjustedin accordance with an amount of whiteness desired, with a smaller pitch519 corresponding to whiter appearing oxide layer 514. FIG. 5C shows atop view of part 520 having equidistant spots 526 within oxide layer 524that are arranged in a staggered configuration spaced an averagedistance 529 apart from each other. Distance 529 can be adjusted inaccordance with an amount of whiteness desired, with smaller distances529 corresponding to whiter appearing oxide layer 524. Note that thepatterns of spots shown in FIGS. 5A-5C are merely exemplary and that anysuitable pattern of spots can be formed within an oxide layer. Forexample, in other embodiments, the spots are spaced a substantiallyrandom distances from each other.

FIG. 6A shows part 600, which includes oxide layer 604 disposed onsubstrate 602. Oxide layer 604 has a substantially continuous line 606that includes a continuous crystalline metal oxide portions orcontinuous line of cracks. Line 606 can be formed using a continuouslaser beam or a pulsed laser beam. For example, a continuous laser beamcan be continuously scanned across top surface 608 to form continuousline 606. A pulsed laser beam can be scanned incrementally over topsurface 608 forming a substantially continuous line 606. FIGS. 6B and 6Cshow top views of parts 610 and 620, respectively, having differentpatterns of lines of crystalline metal oxide portions or cracks. FIG. 6Bshows a top view of part 610 having equidistant parallel lines 616within oxide layer 612. Adjacent lines 626 may be equidistant withrespect to each other. Lines 616 are spaced an average distance 614apart from each other. Distance 614 can be chosen such that the overallappearance of oxide layer 612 is white as viewed from a top surface ofoxide layer 612. Distance 614 can be adjusted in accordance with anamount of whiteness desired, with smaller distances 614 corresponding towhiter appearing oxide layer 612.

FIG. 6C shows a top view of part 620 having equidistant lines 626 ofcrystalline metal oxide portions or cracks that are arranged in acrosshatched pattern. Lines 626 are spaced an average distance 624 apartfrom each other, with some of the lines 626 arranged in a parallelorientation with respect to each other and other lines 626 arranged in aperpendicular orientation with respect to each other, thereby formingthe crosshatched pattern. Distance 624 can be chosen such that theoverall appearance of oxide layer 622 is white as viewed from a topsurface of oxide layer 622. Distance 624 can be adjusted in accordancewith an amount of whiteness desired, with smaller distances 624corresponding to whiter appearing oxide layer 622. Note that thepatterns of lines of crystalline metal oxide portions or cracks shown inFIGS. 6A-6C are merely exemplary and that any suitable pattern of linescan be formed within an oxide layer. For example, in other embodiments,the lines are spaced at substantially random distances from each other.

The crystalline metal oxide portions or cracks can be positioned at anysuitable depth within an oxide layer. To illustrate, FIGS. 7A-7C showcross section views of different parts 700, 710, and 720, respectively,which have spots of crystalline metal oxide portions or cracks atdifferent depths within oxide layers. FIG. 7A shows a cross section viewof part 700 having spots 706 within oxide layer 704, which is positionedover substrate 702. Spots 706 are situated an average distance or depth709 from top surface 708 of oxide layer 704. Depth 709 can be adjustedin accordance with an amount of whiteness desired of oxide layer 704. Insome embodiments, the smaller depths 709 correspond to a whiterappearing oxide layer 704. FIG. 7B shows a cross section view of part710 having spots 716 of crystalline metal oxide portions or crackswithin oxide layer 714, which is positioned over substrate 712. Spots716 are situated an average depth 719 as measured from top surface 718of oxide layer 704. As shown, spots 716 are positioned at a fartherdepth within oxide layer 714 with respect to top surface 718 compared tospots 706 of part 700. In some embodiments, the larger average depth 719will result in oxide layer 714 of part 710 having a less whiteappearance compared to oxide layer 704 of part 700. This can be due todifferent observer viewing angles of spots 706 and spots 716 as viewedfrom top surfaces 708 and 718, respectively.

FIG. 7C shows a cross section view of part 720 having a first layer ofspots 726 of crystalline metal oxide portions or cracks and a secondlayer of spots 727 of crystalline metal oxide portions or cracks withinoxide layer 724, which is positioned over substrate 722. First layer ofspots 726 are situated an average depth 731 from top surface 728 ofoxide layer 724. Second layer of spots 727 are situated an average depth732, larger than average depth 731, from top surface 728 of oxide layer724. In some embodiments, oxide layer 724 of part 720 will have a largeramount of crystalline metal oxide portions or cracks and appear whiterthan each of oxide layer 714 of part 710 and oxide layer 704 of part700. First layer of spots 726 can be arranged in a staggered or parallelorientation with respect to second layer of spots 727. Note that thedepth of the spots of crystalline metal oxide portions or cracks shownin FIGS. 7A-7C are merely exemplary and that any suitable depth andnumber of layers of spots can be formed within an oxide layer. Forexample, in other embodiments, three or more layers of spots are formedwithin an oxide layer.

FIG. 8 shows flowchart 800 indicating a method for forming a white oxidelayer using melting processes in accordance with described embodiments.At 802, at least a portion of an oxide layer is melted. The oxide layercan be formed using any suitable technique and can have any suitablemicrostructure. In some embodiments, the oxide layer is formed using ananodizing process to form a largely amorphous metal oxide structure. Theoxide layer can be formed at any suitable thickness. In someembodiments, the oxide layer has a thickness ranging from about 5micrometers and about 60 micrometers. In some embodiments, the oxidelayer has a thickness ranging from about 10 micrometers and about 30micrometers. In some embodiments, the oxide layer is planarized in orderto form a uniform top surface to the oxide layer. The melting can beperforming using any suitable process. In some embodiments, the meltingoccurs by directing a laser beam at the oxide layer such that alocalized portion of the oxide layer is heated at a temperaturesufficient to reach a melting temperature of the metal oxide material.

At 804, the at least one melted portion of the oxide layer is allowed tocool, thereby forming light diffusing surfaces within the oxide layer.In some embodiments, the cooling process causes the metal oxide materialto re-solidify in crystalline form. In some embodiments, the coolingprocess causes the metal oxide material to crack. In some embodiments,the cooling process forms both crystalline metal oxide and forms cracks.The crystalline metal oxide and/or cracks have surfaces that can causelight incident on the top surface of the oxide layer to diffuselyreflect, imparting a white appearance to the oxide layer. In someembodiments, the crystalline metal oxide or cracks are formed beneaththe top surface of the oxide layer, thereby leaving a continuous,un-affected and un-cracked top surface. The crystalline metal oxideportions or cracks can be formed in any suitable pattern within theoxide layer and at any suitable depth within the oxide layer. In someembodiments, the depth and pattern of crystalline metal oxide portionsor cracks is chosen to achieve a predetermined whiteness of the oxidelayer.

As described above, specular reflection involves reflection of light inone direction. Objects that specularly reflect light will have amirror-like quality. In contrast, diffuse reflection involves scatteringof light resulting in objects appearing white. In some applications, itcan be desirable for an oxide film to both diffusely and specularlyreflect visible light, resulting in a white and bright appearance. Therelative amount of diffuse reflection and specular reflection can beadjusted to accomplish a particular white and bright appearance. Toillustrate, FIG. 9A shows a cross section view of part 900, whichincludes oxide layer 904 positioned on substrate 902. Oxide layer 904includes first portion 910 and second portion 912. First portion 910 hasspots 906 of crystalline metal oxide or cracks that diffusely reflectincoming visible light. For instance, light ray 914 entering top surface908 of oxide layer 904 reflects off spots 906 and exits top surface 908at a first angle. Light ray 916 entering top surface 908 of oxide layer904 reflects off spots 906 and exits top surface 908 at a second anglethat is different than the first angle. In this way, spots 906 diffuselyreflect light incident top surface 908 and impart a white appearance tofirst portion 910 of oxide layer 904.

Second portion 912 does not substantially include any spots ofcrystalline metal oxide or cracks and is substantially translucent ortransparent. As such, at least some light incident top surface 908 cantravel through second portion 912 and reflect off top surface 922 ofsubstrate 902. If top surface 922 is a specularly reflective surface,such as a polished shiny metal surface, light will reflect off of topsurface 922. For instance, light ray 918 entering top surface 908travels through oxide layer 904, reflects off top surface 922, and exitstop surface 908 at a first angle. Light ray 920 entering top surface 908travels through oxide layer 904, reflects off top surface 922, and exitstop surface 908 also at the first angle. In this way, the specularlyreflective top surface 922 of substrate 902 can be visible throughsecond portion 912 of oxide layer 904 and impart a shiny mirror-likeshine to the portion of part 900 corresponding to second portion 912.This combination of diffuse and specular reflection gives part 900 awhite and bright appearance. The relative amount of diffuse and specularreflection can be adjusted by choosing an amount of portions of oxidelayer 904 having spots 906. The amount of specular reflection of part900 can be measured using any of a number of light reflectionmeasurement techniques. In some embodiments, a spectrometer configuredto measure specular light intensity at specified angles can be used. Themeasure of specular light intensity is associated with an amount oflightness and L value, as described above. In some embodiments, theamount of specular reflection is compared against a standard to achievea predetermined amount of specular reflection for part 900.

FIG. 9B shows flowchart 950 indicating a method for tuning a meltingprocess for producing a white oxide film having a target amount ofdiffuse and specular reflectance. At 952, crystalline metal oxide orcracks are formed within an oxide film creating a white oxide film. Insome embodiments, a laser melting procedure is used. The laser will havea set of parameters, such as wavelength, spot size and depth of focus,appropriate for melting metal oxide material within the oxide layer andforming crystalline metal oxide portions or cracks. At 954, the amountof specular reflectance of the white oxide film is measured. Aspectrometer may be used. The spectrometer can measure the spectralreflectance at a defined angle and generate a corresponding reflectancespectrum. At 956, the measured specular reflectance of the white oxidefilm is compared to a target specular reflectance measurement. Thetarget specular reflectance measurement will correspond to a white oxidefilm having a desired amount of specular and diffuse reflection.

At 958, it is determined from the comparison whether the amount ofspecular reflectance of the white oxide film is too high. If thespecular reflectance is too high, at 960, a new cracking process isdesigned that has an increased amount of diffuse reflectance. The amountof diffuse reflectance can be increased by increasing the amount ofcrystalline metal oxide portions or cracks within the oxide film, orchanging the positions of the crystalline metal oxide portions or crackswithin the oxide film, such as described above with reference to FIGS.5-7. Then, returning to 952, an additional white oxide film is formedusing the new melting process parameters. If the specular reflectance isnot too high, at 962, it is determined from the comparison whether theamount of specular reflectance of the white oxide film is too low. Ifthe specular reflectance is too low, at 964, a new melting process isdesigned that has a decreased amount of diffuse reflectance. The amountof diffuse reflectance can be decreased by decreasing the amount ofcrystalline metal oxide portions or cracks within the oxide film, orchanging the positions of the crystalline metal oxide portions or crackswithin the oxide film, such as described above with reference to FIGS.5-7. Then, returning to 952, an additional white oxide film is formedusing the new melting process parameters. If the specular reflectance isnot too low, the white oxide film has a target amount of diffuse andspecular reflectance.

In some embodiments, the underlying substrate surface has a differentsurface quality than a specularly reflective shine. For example, theunderlying substrate can have a roughened surface that absorbs incidentlight and therefore has a dark or black appearance. FIG. 10 shows across section view of part 1000, which includes oxide layer 1004positioned on substrate 1002, which has rough top surface 1022. Roughtop surface 1022 can be formed using any suitable process, such as alaser marking technique. In a laser marking technique, the laserwavelength and other process parameters are tuned to travel throughoxide layer 1004 and roughen rough top surface 1022 of substrate 1002.Rough top surface 1022 can absorb anywhere from some light tosubstantially all light incident top surface 1008. For instance, lightrays 1014 and 1016 entering top surface 1008 travel through oxide layer1004 and become absorbed by rough top surface 1022. Oxide layer 1004also includes spots 1006 of crystalline metal oxide portions or cracksthat can diffusely reflect incoming visible light. For instance, lightray 1018 entering top surface 1008 reflects off spots 1006 and exits topsurface 1008 at a first angle. Light ray 1020 entering top surface 1008reflects off spots 1006 and exits top surface 1008 at a second anglethat is different than first angle. The combination of light absorptionand light diffuse gives part 1000 a unique color and appearance that canbe adjusted by modifying the amount of roughness of rough top surface1022 and the amount of spots 1006 within oxide layer 1004.

In some embodiments, the cracks are formed in a pattern such that aportion of the part appears white while other portions of the partappear as a different color. FIG. 11 shows a top view of part 1100having different colored portions in accordance with describedembodiments. Part 1100 includes an oxide layer 1104 that has a topsurface corresponding to a top surface of part 1100. Oxide layer 1104includes first portion 1102, which has a different appearance thansurrounding second portion 1103. First portion 1102 has spots 1106 ofcrystalline metal oxide portions or cracks that give first portion 1102a white appearance. In some embodiments, first portion 1102 is in theshape of a design or logo. In some embodiments, second portion 1103 doesnot substantially include any spots of crystalline metal oxide portionsor cracks and, therefore, has a different color than first portion 1102.In some embodiments, second portion 1103 includes spots of crystallinemetal oxide portions or cracks and has a different shade of whitecompared to first portion 1102. Note that in embodiments where a laserbeam is used to form spots 1106, spots 1106 can be formed without theuse of a masking process. That is, the laser system can be tuned to scanor raster select portions of an oxide layer, such as first portion 1102,without the use of a mask.

In some embodiments, second portion 1103 is substantially translucent ortransparent, thereby allowing the underlying metal substrate to show. Insome embodiments, the underlying substrate is an aluminum or aluminumalloy and has a silver or grey color that can at least be partiallyvisible through second portion 1103. In some embodiments, the underlyingsubstrate has a reflective surface (e.g., mirror-like shine) that is atleast partially visible through second portion 1103, as described above.In some embodiments, second portion 1103 has one or more coloring agentsto impart a color to second portion 1103. For example, second portion1103 can include one or more dye, metal, or metal oxide agents infusedwithin the pores of the oxide material of second portion 1103. In someembodiments, first portion 1102 includes one or more coloring agentsthat can enhance its white color. For example, first portion 1102 canhave one or more dye, metal, and metal oxide agents infused within thepores of the oxide material of first portion 1102.

In some embodiments, the cracks are formed subsequent to an oxide filmdyeing process such that forming the cracks modifies the color of thedye and results in an oxide film having a different color than impartedby the dye itself. To illustrate, FIG. 12 shows a top view of part 1200having different dyed portions in accordance with described embodiments.Part 1200 includes an oxide layer 1204 that has a top surfacecorresponding to a top surface of part 1200. Oxide layer 1204 includesfirst portion 1202, which has a different appearance than surroundingsecond portion 1203. In some embodiments, first portion 1202 is in theshape of a design or logo. Both first portion 1202 and second portion1203 have one or more of the same dye infused therein. However, firstportion 1202 has spots 1206 of crystalline metal oxide portions orcracks. During the formation of spots 1206, portions of the metal oxidematerial within first portion 1202 are heated and melted, as describedabove. This localized heating can cause the infused dye within firstportion 1202 to change color. In some embodiments, the localized heatingcauses bleaching or lightening of the dye, thereby giving first portion1202 a lighter color compared to surrounding second portion 1203. As aresult, part 1200 has a varied colored look.

FIG. 13 shows flowchart 1300 indicating a method for forming an oxidelayer on a part having a particular optical quality using the meltingmethods described herein. The optical quality can be a desired color ora desired brightness. At 1302, light diffusing crystalline metal oxideportions or cracks are formed within an oxide layer. The light diffusingcrystalline metal oxide portions or cracks can be formed using anysuitable method. In some embodiments, the light diffusing crystallinemetal oxide portions or cracks are formed by directing a laser beam at atop surface of the oxide layer such that energy from the laser beam istransferred as heat to melt a portion of the metal oxide material withinthe oxide layer. Crystalline metal oxide portions or cracks form withinthe oxide layer as the metal oxide material cools and contracts. In someembodiments, the laser is focused such that the crystalline metal oxideportions or cracks form entirely below a top surface of the oxide layerleaving the top surface of the oxide layer substantially crack-free andcontinuous. In some embodiments, the oxide layer has a smooth andspecularly reflective top surface. In some embodiments, the oxide layerhas one or more dyes or other coloring agents infused therein. In someembodiments, the heat from the laser beam modifies the color of the dyesor other coloring agents, thereby modifying the color of the oxidelayer.

At 1304, an optical quality of the oxide layer is measured after themelting treatment. A color of the treated oxide layer can be measuredusing any suitable colorimetric methods including, but not limited to,use of a colorimeter, spectrometer and/or a spectrophotometer. Thebrightness can be measured using any suitable method including, but notlimited to, photometric techniques and/or radiometric techniques. At1306, the optical quality measurement of the treated oxide layer iscompared to a target optical quality measurement. In some embodiments,the target optical quality is obtained by measuring the optical qualitymeasurements of a sample that has a predetermined desired opticalquality, such as a predefined color or brightness measurement. At 1308,it is determined whether the measured optical quality of the treatedoxide layer has achieved the target optical quality. If the targetoptical quality has not been achieved, at 1310, a new process is designwherein the amount or position of the light diffusing within an oxidelayer is adjusted. Then, at 1302, another oxide layer is formed usingthe new process. This process is repeated until at 1308, the targetoptical quality is achieved and the process of flowchart 1300 iscomplete.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the describedembodiments. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice the describedembodiments. Thus, the foregoing descriptions of the specificembodiments described herein are presented for purposes of illustrationand description. They are not target to be exhaustive or to limit theembodiments to the precise forms disclosed. It will be apparent to oneof ordinary skill in the art that many modifications and variations arepossible in view of the above teachings.

What is claimed is:
 1. An enclosure for a portable electronic device,the enclosure comprising: a substrate that includes a metal; and a metaloxide layer disposed over the substrate, the metal oxide layer having anexterior surface and crystalline portions that include at least (i) afirst light-reflective facet oriented at a first angle relative to theexterior surface, and (ii) a second light-reflective facet oriented at asecond angle relative to the exterior surface that is different than thefirst angle.
 2. The enclosure of claim 1, wherein the crystallineportions are separated by a separation distance that is between 1micrometer to 10 micrometers.
 3. The enclosure of claim 1, wherein themetal oxide layer includes an oxidized portion of the metal having afirst index of refraction, and the crystalline portions have a secondindex of refraction that is different than the first index ofrefraction.
 4. The enclosure of claim 1, wherein visible light thatpasses through the metal oxide layer, impinges on at least the first andsecond light-reflective facets, and is diffusely reflected out of themetal oxide layer at different angles, imparts a white appearance to themetal oxide layer.
 5. The enclosure of claim 1, wherein the substratehas a surface having a mirror finish, and the mirror finish is visiblethrough the exterior surface of the metal oxide layer.
 6. The enclosureof claim 1, wherein the metal oxide layer includes metal oxide material,and the crystalline portions include re-solidified portions of the metaloxide material.
 7. A metal part for a consumer electronic product,comprising: a substrate; and an anodic layer that has an exteriorsurface and is disposed over the substrate, the anodic layer including ametal oxide material having a first refractive index that is separatedby light-reflective facets having a second refractive index differentthan the first refractive index, wherein the light-reflective facetsinclude at least (i) a first light-reflective facet oriented at a firstangle relative to the exterior surface, and (ii) a secondlight-reflective facet oriented at a second angle relative to theexterior surface that is different than the first angle.
 8. The metalpart of claim 7, wherein when visible light is incident upon theexterior surface, the first and second light-reflective facets cause thevisible light to diffusely reflect out of the anodic layer at differentangles of reflection.
 9. The metal part of claim 7, wherein thelight-reflective facets are disposed within crystalline portions, andthe crystalline portions are separated by at least a separationdistance.
 10. The metal part of claim 9, wherein the separation distancebetween the crystalline portions is between 1 micrometer to 10micrometers.
 11. The metal part of claim 10, wherein the separationdistance contributes to imparting a white appearance to the anodiclayer.
 12. The metal part of claim 9, wherein the crystalline portionsare equidistantly spaced apart from each other.
 13. A method for formingan enclosure for a portable electronic device having a white appearance,the method comprising: forming a metal oxide layer over a substrate,wherein the metal oxide layer includes an exterior surface; and formingcrystalline portions from metal oxide material of the metal oxide layer,wherein the crystalline portions include at least (i) a firstlight-reflective facet oriented at a first angle relative to theexterior surface, and (ii) a second light-reflective facet oriented at asecond angle relative to the exterior surface that is different than thefirst angle.
 14. The method of claim 13, wherein forming the crystallineportions includes: melting pre-determined portions of the metal oxidematerial by using a laser beam; and causing the pre-determined portionsthat were melted to solidify to form the crystalline portions.
 15. Themethod of claim 14, wherein causing the pre-determined portions tosolidify causes cracks to form within the metal oxide layer.
 16. Themethod of claim 13, wherein the crystalline portions are separated by aseparation distance that is between 1 micrometer to 10 micrometers. 17.The method of claim 13, wherein the metal oxide material ischaracterized as having a first index of refraction, and thelight-reflective facets are characterized as having a second index ofrefraction that is different than the first index of refraction.
 18. Theenclosure of claim 1, wherein the metal oxide layer is transparent sothat the crystalline portions are visible through the exterior surfaceof the metal oxide layer.
 19. The method of claim 13, wherein thecrystalline portions are formed from re-solidified metal oxide material.